Phosphate optical glass

ABSTRACT

The invention including phosphate optical glass with refractivity ranging from 1.93 to 1.95 and the Abbe number ranging from 16 to 19, with a low liquidus temperature. The phosphate optical glass, including: 5 to 25 wt % of NaPO 3 , 1 to 20 wt % of KPO 3 , 2 to 15 wt % of P 2 O 5 , 0 to 5 wt % of BaO, 0 to 10 wt % of Ba(PO 3 ) 2 , more than 0 but less than 2 wt % of B 2 O 3 , 5 to 25 wt % of TiO 2 , 35 to 55 wt % of Nb 2 O 5 , and 0 to 5 wt % of SiO 2 . Refractivity of phosphate optical glass can reach 1.93 to 1.95, the Abbe number can reach 16 to 19, the liquidus temperature is below 1,120° C., the processing property during melting is good, the glass surface is unlikely to be devitrified during the processing of the glass, and can be formed easily.

FIELD OF THE INVENTION

The invention relates to a phosphate optical glass.

RELATED ART

With the rapid development of novel optoelectronic products, an optical glass with the refractivity ranging from 1.93 to 1.95 and the Abbe number ranging from 16 to 19 is in great demand. According to the relation between the refractivity and the Abbe number, the optical glass with the refractivity ranging from 1.93 to 1.95 and the Abbe number ranging from 16 to 19 is not suitable for an SiO₂—Nb₂O₅—TiO₂—BaO—R₂O formulation system due to the fact that the glass system in this case is liable to be extremely unstable, uniform products with good inherent quality are unavailable, and the transmissivity is unsatisfactory. However, a phosphate formulation system can realize obvious stability of the glass and guarantee the transmissivity of visible light.

Besides, during the melting of phosphate glass, it is ideal to minimize the liquidus temperature. In other words, to realize stable production of the phosphate glass, a formulation system capable of minimizing the liquidus temperature shall be adopted during the design of the glass formulation. If the liquidus temperature of the glass is high, the glass during the melting will be formed difficulty, the processing property will be poor, and crystals will appear on the surface of the glass during the following secondary processing of the glass, which will affect the surface quality of the processed product.

DISCLOSURE OF THE INVENTION

A technical problem to be solved by the invention is to provide a phosphate optical glass with the refractivity ranging from 1.93 to 1.95 and the Abbe number ranging from 16 to 19, which has a minimized the liquidus temperature.

To solve the technical problem, the invention provides the phosphate optical glass, consisting essentially of: 5 to 25 wt % of NaPO₃, 1 to 20 wt % of KPO₃, 2 to 15 wt % of P₂O₅, 0 to 5 wt % of BaO, 0 to 10 wt % of Ba(PO₃)₂, more than 0 but less than 2 wt % of B₂O₃, 5 to 25 wt % of TiO₂, 35 to 55 wt % of Nb₂O₅, and 0 to 5 wt % of SiO₂.

Furthermore, the content of B₂O₃ is more than 0 but less than 1 wt %.

Furthermore, the content of B₂O₃ is more than 0 but less than 0.8 wt %.

Furthermore, the content of TiO₂ is 10 to 20 wt %.

Furthermore, the content of TiO₂ is more than 14% but less than 18 wt %.

Furthermore, the content of Nb₂O₅ is 40 to 48 wt %.

Furthermore, the content of NaPO₃ is 10 to 20 wt %.

Furthermore, the content of KPO₃ is 5 to 15 wt %.

Furthermore, the content of Ba(PO₃)₂ is 1 to 5 wt %.

Furthermore, the content of P₂O₅ is 5 to 10 wt %.

Furthermore, the content of BaO is 0.1 to 2 wt %.

Furthermore, the content of SiO₂ is 0.1 to 2 wt %.

Furthermore, the total content of NaPO₃ and KPO₃ is 20 to 30 wt %.

An optical element is formed of said phosphate optical glass.

The phosphate optical glass provided by the invention is advantageous in that the refractivity of the glass can reach 1.93 to 1.95, the Abbe number can reach 16 to 19, the liquidus temperature is below 1,120° C., the processing property during the melting is good, the glass can be formed easily, and the surface of the glass is unlikely to be devitrified during the following processing of the glass.

EMBODIMENTS

Through a great number of researches and experiments, the present inventor found that a glass composition with low liquidus temperature and required refractivity and Abbe number is available through designing specific glass formulation, especially controlling the content of B₂O₃ in the formulation system.

The invention provides a phosphate optical glass, the invention provides the phosphate optical glass, consisting essentially of: 5 to 25 wt % of NaPO₃, 1 to 20 wt % of KPO₃, 2 to 15 wt % of P₂O₅, 0 to 5 wt % of BaO, 0 to 10 wt % of Ba(PO₃)₂, more than 0 but less than 2 wt % of B₂O₃, 5 to 25 wt % of TiO₂, 35 to 55 wt % of Nb₂O₅, and 0 to 5 wt % of SiO₂.

NaPO₃ is an essential component of the phosphate optical glass, which can promote stable formation of the glass, effectively lower the glass melting temperature and guarantee high transmissivity in a visible region, so the content of NaPO₃ shall be at least 5 wt %, otherwise said effects are unavailable. However, when the content exceeds 25 wt %, the optical performance with high refractivity cannot be realized. Therefore, the content of NaPO₃ in the invention is 5 to 25 wt %, preferably 10 to 20 wt %, more preferably 12 to 16 wt %.

Also as an essential component of the phosphate optical glass, KPO₃ can more effectively promote stable formation of the glass when being mixed with NaPO₃, which is capable of lowering the glass melting temperature and guaranteeing high transmissivity in the visible region, so the content of KPO₃ shall be at least 1 wt %, otherwise said effects are unavailable. However, the devitrification resistance of the glass is liable to be degraded when the content of KPO₃ exceeds 20 wt %, so the content of KPO₃ is 1 to 20 wt %, preferably 5 to 15 wt %, more preferably 8 to 12 wt %.

The present inventor also found that, the thermal shock resistance of the glass can be improved via controlling the content of NaPO₃ and KPO₃ due to the fact that the thermal expansion coefficient of the glass is liable to be increased to result in breaking during the following processing when the total content of NaPO₃ and KPO₃ exceeds 35 wt %. Therefore, the total content of NaPO₃ and KPO₃ is 6 to 35 wt %, more preferably 20 to 30 wt %.

As a framework component of the phosphate formulation system, P₂O₅ is mainly used to lower the melting temperature and improve the transmissivity of the glass. However, the effects are not obvious when the content of P₂O₅ is less than 2 wt %, and the refractivity of the glass is liable to be significantly decreased and the required optical performance is unavailable when the content of P₂O₅ exceeds 15 wt %. Therefore, the content of P₂O₅ is 2 to 15 wt %, preferably 5 to 10 wt %.

After an appropriate amount of BaO is used, the devitrification property of the glass can be improved, the Abbe number of the glass provided by the invention can be adjusted, and the glass forming property during the melting can be better. Therefore, the content of BaO is 0 to 5 wt %, preferably 0.1 to 2 wt %.

Ba(PO₃)₂ can improve the devitrification resistance of the glass simultaneously with adjust the refractivity of the glass. In the invention, an appropriate amount of Ba(PO₃)₂ can be used for adjusting phosphoric acid and/or BaO in the formulation system; besides, after Ba(PO₃)₂ is used in the formulation system, the content of P₂O₅ in the system can be minimized due to the fact that P₂O₅ is more active than Ba(PO₃)₂ to result in instable melting of the glass. However, high dispersion of the glass cannot be realized when the content of Ba(PO₃)₂ exceeds 10 wt %, so the content of Ba(PO₃)₂ in the glass provided by the invention is 0 to 10 wt %, preferably 1 to 5 wt %, more preferably more than 2 wt % but less than 4 wt %.

B₂O₃ is an effective component for improving the melting behavior and reducing the melting temperature of the glass. In addition, a little amount of B₂O₃ used in the invention significantly reduces the liquidus temperature of the glass; however, when the content of B₂O₃ exceeds 2 wt % or B₂O₃ is not used, the effect of lowering the liquidus temperature of the glass is liable to be poor obviously. Therefore, the effect of lowering the liquidus temperature of the glass is best when the content of B₂O₃ is more than 0 but less than 2 wt %, preferably more than 0 but less than 1 wt %, more preferably more than 0 but less than 0.8 wt %.

Nb₂O₅ is an effective component for realizing high refractivity and adjusting the Abbe number of the glass simultaneously with inhibiting devitrification. In addition, the present inventor found that the thermal expansion coefficient of the glass can be effectively reduced and the thermal shock resistance of the glass can be enhanced by optimizing the content of Nb₂O₅. Said effects are unavailable when the content of Nb₂O₅ is less than 35 wt %, but the glass cost is liable to be high devitrification is liable to be occur when the content of Nb₂O₅ exceeds 55 wt %. Therefore, the content of Nb₂O₅ is 35 to 55 wt %, preferably 40 to 48 wt %, more preferably 45 to 48 wt %.

TiO₂ is an essential component for realizing optical performance indexes of the glass, which can effectively reduce the thermal expansion coefficient of the glass the same as Nb₂O₅. Due to high cost of Nb₂O₅, the content of TiO₂ is appropriately increased to realize the optical performance and strong thermal shock resistance, thereby effectively decreasing the content of Nb₂O₅. The required effects are unavailable when the content of TiO₂ is less than 5 wt %, but the devitrification resistance and coloring degree of the glass are liable to be poor when the content of TiO₂ exceeds 25 wt %. Therefore, the content of TiO₂ in the invention is 5 to 25 wt %, preferably 10 to 20 wt %, more preferably more than 14 wt % but less than 18 wt %.

SiO₂ is an optional component of the glass provided by the invention, and an appropriate amount of SiO₂ also can effectively reduce the thermal expansion coefficient, enhance the chemical resistance and improve the stability of the glass. However, the glass is liable to be refractory when the content of SiO₂ exceeds 5 wt %. Therefore, the content of SiO₂ is 0 to 5 wt %, preferably 0.1 to 2 wt %, more preferably 0.1 to 1 wt %.

For the phosphate glass composition, bubbles will be remained and are difficulty to be exhausted completely due to over low melting temperature, so a fining agent Sb₂O₃ is usually used during the melting. However, Sb₂O₃ is always required to be used together with nitrates, which is liable to increase the discharge of nitrogen oxides during the melting of the glass composition, thus causing certain pollution to the environment. To control the pollutant emission in the air, Ba(PO₃)₂ and BaO are used in the invention to improve the activity of the glass, so the melting of the glass composition can still be realized without using the fining agent Sb₂O₃.

The refractivity of the optical glass provided by the invention ranges from 1.93 to 1.95, and the Abbe number ranges from 16 to 19; preferably, the refractivity of the optical glass provided by the invention ranges from 1.94 to 1.95, and the Abbe number ranges from 17 to 19.

To realize stable production of the glass provided by the invention, it is important to control the liquidus temperature of the glass below 1,120° C. The liquidus temperature of the glass is preferably below 1,100° C., more preferably below 1,090° C.

For the glass provided by the invention, the thermal expansion coefficient α (at 20 to 300° C.) is less than 59×10⁻⁷/° C., preferably less than 57×10⁻⁷/° C., more preferably less than 53×10⁻⁷/° C.

The invention also provides an optical element formed of said glass, which has various properties of said glass.

The performance parameters of the glass provided by the invention are measured as follows:

The refractivity (nd) and the Abbe number are measured as per the Method for Testing the Refractivity and Dispersion Coefficient of Colorless Optical Glass (GB/T 7962.1-1987).

The devitrification property of the glass is measured by a gradient-furnace method which comprises the following steps: processing the glass into samples (180 mm×10 mm×10 mm), polishing lateral sides, placing the samples into a furnace having a temperature gradient, taking out the samples after keeping the temperature for 4 hours, and observing the devitrification of glass under a microscope, wherein the maximum temperature corresponding to the appearance of crystals is the liquidus temperature of the glass.

The thermal expansion coefficient α (at 20 to 120° C.) refers to the elongation in unit length of the glass per degree rise within a range of 20 to 120° C., which is measured as per the method specified in GB/T7962.16-1987.

A method for preparing the glass provided by the invention has no special restrictions, just conducted as per the method well known to technical personnel in the field. The optical glass is obtained by melting the raw materials, settling, homogenizing, cooling, casting into a preheated metal mold and annealing. Raw materials such as NaPO₃, KPO₃ and Ba(PO₃)₂ that are stable in state are used during the preparation of the glass, thus realizing stable production.

The glass provided by examples 1 to 20 in the invention is prepared by the following steps: proportionally weighing the raw materials corresponding to the glass composition in embodiments 1 to 20, mixing fully and then adding into a platinum crucible, melting at 1,000 to 1,300° C., settling, homogenizing and then cooling; casting the fused glass into the preheated metal mold at about 550 to 600° C.; and then placing the fused glass cast into the preheated metal mold together with the metal mold into an annealing furnace, annealing slowly to obtain the glass, and measuring related parameters of the glass. The glass provided by examples 1 to 20 has advantages that no crystals appear on the surface during the following secondary processing and the surface quality is good.

The refractivity, Abbe number, liquidus temperature and thermal expansion coefficient of the glass provided by examples 1 to 20 are illustrated in Tables 1 to 4.

TABLE 1 Examples 1 to 5 1 2 3 4 5 Composition NaPO₃ 15 16.3 17.2 18.5 9.1 (wt %) KPO₃ 9.8 8.5 7.7 6.4 15 Ba(PO₃)₂ 4.9 3.4 2.6 4.1 7.9 P₂O₅ 7.1 8.8 9.6 7.9 4.5 BaO 0.1 0.4 0.6 1.2 1.7 B₂O₃ 0.1 0.3 0.4 0.7 0.9 TiO₂ 14.9 15.9 22.5 21.6 15.8 Nb₂O₅ 45.1 46.4 39.4 38.9 43.4 SiO₂ 3 0.7 1.7 Total 100 100 100 100 100 Performance nd 1.945 1.947 1.931 1.930 1.940 Parameters vd 16.1 16.3 17.0 18.4 18.7 Liquidus 1108 1107 1109 1100 1120 temperature (° C.) Thermal 58 × 10⁻⁷/ 59 × 10⁻⁷/ 54 × 10⁻⁷/ 55 × 10⁻⁷/ 58 × 10⁻⁷/ expansion ° C. ° C. ° C. ° C. ° C. coefficient α (at 20 to 120° C.)

TABLE 2 Examples 6 to 10 6 7 8 9 10 Composition NaPO₃ 10 11.3 12.1 13.4 14.7 (wt %) KPO₃ 14.7 13.2 12.1 11.8 10.3 Ba(PO₃)₂ 7.3 6.5 5.2 5.7 3.3 P₂O₅ 5 5.6 6.4 6.8 7.5 BaO 2 2.2 2.4 3.1 0.5 B₂O₃ 0.7 0.8 0.7 0.6 0.7 TiO₂ 19.4 18.3 17 16.5 15.9 Nb₂O₅ 40.4 41.5 44.1 42.1 46.6 SiO₂ 0.5 0.6 0.5 Total 100 100 100 100 100 Performance nd 1.938 1.942 1.948 1.941 1.948 Parameters vd 18.02 17.81 17.94 18.43 17.96 Liquidus 1102 1100 1103 1105 1105 temperature (° C.) Thermal 57 × 10⁻⁷/ 55 × 10⁻⁷/ 56 × 10⁻⁷/ 55 × 10⁻⁷/ 55 × 10⁻⁷/ expansion ° C. ° C. ° C. ° C. ° C. coefficient α (at 20 to 120° C.)

TABLE 3 Examples 11 to 15 11 12 13 14 15 Composition NaPO₃ 14.5 15.3 14.8 15 13.7 (wt %) KPO₃ 9.8 10.8 11.5 10.1 11.9 Ba(PO₃)₂ 3.1 3.8 4.2 3 5.1 P₂O₅ 7.5 8.3 9.1 7.1 6.8 BaO 0.8 1.1 2.3 0.4 1.5 B₂O₃ 0.7 0.8 0.2 0.4 0.5 TiO₂ 16.2 13.8 16.7 15.3 15.5 Nb₂O₅ 47 43.9 41.2 48.7 45 SiO₂ 0.4 2.2 Total 100 100 100 100 100 Performance nd 1.948 1.939 1.940 1.949 1.938 Parameters vd 17.96 17.70 17.98 17.97 18.16 Liquidus 1103 1095 1110 1107 1108 temperature (° C.) Thermal 59 × 10⁻⁷/ 56 × 10⁻⁷/ 55 × 10⁻⁷/ 59 × 10⁻⁷/ 59 × 10⁻⁷/ expansion ° C. ° C. ° C. ° C. ° C. coefficient α (at 20 to 120° C.)

TABLE 4 Examples 16 to 20 16 17 18 19 20 Composition NaPO₃ 18.7 19.4 13.6 14.4 10.1 (wt %) KPO₃ 9.8 8.1 10.6 11.3 12.8 Ba(PO₃)₂ 2.5 5.4 5.4 5.1 P₂O₅ 11.5 12.6 8.5 9.3 13 BaO 4.6 4.4 4.7 4 B₂O₃ 0.6 1.5 0.4 1 0.8 TiO₂ 13.8 8.5 7.4 6.1 4.2 Nb₂O₅ 43.1 45.3 49.4 47.8 50 SiO₂ 0.3 Total 100 100 100 100 100 Performance nd 1.948 1.940 1.942 1.931 1.938 Parameters vd 18.05 17.84 18.04 18.15 17.96 Liquidus 1090 1120 1112 1120 1095 temperature (° C.) Thermal 59 × 10⁻⁷/ 58 × 10⁻⁷/ 59 × 10⁻⁷/ 59 × 10⁻⁷/ 59 × 10⁻⁷/ expansion ° C. ° C. ° C. ° C. ° C. coefficient α (at 20 to 120° C.)

As illustrated from the examples, the glass and the optical element provided by the invention have low liquidus temperature and thermal expansion coefficient, good stability and thermal shock resistance with no fining agent during the melting, the refractivity ranging from 1.93 to 1.95 and the Abbe number ranging from 16 to 19, which meet requirements of novel optoelectronic products in modern times. 

The invention claimed is:
 1. A phosphate optical glass formed from a raw material mixture consisting essentially of: 5 to 25 wt % of NaPO₃, 1 to 20 wt % of KPO₃, 2 to 15 wt % of P₂O₅, 0 to 5 wt % of BaO, 0 to 10 wt % of Ba(PO₃)₂, more than 0 but less than 2 wt % of B₂O₃, 5 to 25 wt % of TiO₂, 35 to 55 wt % of Nb₂O₅, and 0 to 5 wt % of SiO₂ wherein the phosphate optical glass is free of Sb₂O₃.
 2. The phosphate optical glass according to claim 1, wherein the content of B₂O₃ is more than 0 but less than 1%.
 3. The phosphate optical glass as recited in claim 1, wherein the content of B₂O₃ is more than 0 but less than 0.8%.
 4. The phosphate optical glass as recited in claim 1, wherein the content of TiO₂ is 10 to 20%.
 5. The phosphate optical glass as recited in claim 1, wherein the content of TiO₂ is more than 14% but less than 18%.
 6. The phosphate optical glass as recited in claim 1, wherein the content of Nb₂O₅ is 40 to 48%.
 7. The phosphate optical glass as recited in claim 1, wherein the content of Nb₂O₅ is 45 to 48%.
 8. The phosphate optical glass as recited in claim 1, wherein the content of NaPO₃ is 10 to 20%.
 9. The phosphate optical glass as recited in claim 1, wherein the content of NaPO₃ is 12 to 16%.
 10. The phosphate optical glass as recited in claim 1, wherein the content of KPO₃ is 5 to 15%.
 11. The phosphate optical glass as recited in claim 1, wherein the content of KPO₃ is 8 to 12%.
 12. The phosphate optical glass as recited in claim 1, wherein the content of Ba(PO₃)₂ is 1 to 5%.
 13. The phosphate optical glass as recited in claim 1, wherein the content of Ba(PO₃)₂ is more than 2% but less than 4%.
 14. The phosphate optical glass as recited in claim 1, wherein the content of P₂O₅ is 5 to 10%.
 15. The phosphate optical glass as recited in claim 1, wherein the content of BaO is 0.1 to 2%.
 16. The phosphate optical glass as recited in claim 1, wherein the content of SiO₂ is 0.1 to 2%.
 17. The phosphate optical glass as recited in claim 1, wherein the content of SiO₂ is 0.1 to 1%.
 18. The phosphate optical glass as recited in claim 1, wherein the total content of NaPO₃ and KPO₃ is 20 to 30%.
 19. The phosphate optical glass as recited in claim 1, wherein the total content of NaPO₃ and KPO₃ is 6 to 35%.
 20. The phosphate optical glass as recited in claim 1, wherein the refractivity of said optical glass ranges from 1.93 to 1.95, and the Abbe number ranges from 16 to
 19. 21. The phosphate optical glass as recited in claim 1, wherein the liquidus temperature of said optical glass is controlled below 1,120° C.
 22. An optical element made of the phosphate optical glass according to claim
 1. 